Postpartum depression typically develops within four to six weeks after birth. Researchers believe that changes in estrogen levels make pregnant women more sensitive to the stress hormone cortisol, and the test could help to identify women who have genetic variations that make them unable to correct the hormonal imbalance, according to Professor Dimitris Grammatopoulos, lead researcher at University Hospitals Coventry and Warwickshire NHS Trust.

"There is evidence that if you can identify women at risk early you could treat early or introduce measures to prevent or stop the process of the disease," he says.